RECOVERY OF SCHISTOSOMA-JAPONICUM FROM EXPERIMENTALLY INFECTED-PIGS BY PERFUSION OF LIVER AND MESENTERIC VEINS

An optimized procedure for perfusion of pigs infected with Schistosoma japonicum was developed. The technique involves insertion of a perfus ion influx tube into the thoracic descending aorta, clamping vessels t o parts of the body which did not need to be perfused (the kidneys, hi nd legs, etc.) and placing a collection tube directly into the portal vein. In addition, the clamping technique allows for separate perfusio n of the liver and intestinal veins. The perfusion medium was a sodium citrate buffer (40 degrees C) to which the vasodilator sodium nitropr usside was added. Furthermore, an experiment was conducted to investig ate if the perfusion efficiency, measured by total worm recovery, coul d be increased if praziquantel was administered prior to perfusion. Tw elve pigs were each infected with 1000 S. japonicum cercariae and thei r schistosomes were collected 11 weeks later by separate perfusion of the liver and intestinal veins. Six of these pigs were treated orally with praziquantel one hour before perfusion. In general, the vessels o f the livers and intestines of all pigs were well perfused, judging by the resulting pale colour of the tissues. Worms from praziquantel tre ated pigs were collected within 5 min of perfusion as opposed to appro ximately 20 min in the non-treated pigs. More worms were collected fro m the livers of the praziquantel treated pigs, indicating a hepatic sh ift of schistosomes from the intestinal mesenteries. However, comparab le numbers of worms were retained in the mesenteric veins following pe rfusion in the 2 groups, indicating that manual recovery of schistosom es from the intestinal mesenteries is necessary in addition to perfusi on for obtaining the total worm counts. Another experiment was conduct ed to determine if the intensity and/or duration of infection had an e ffect on the number of worms collected by the perfusion technique. Sev enty-two pigs were allocated into 3 groups of 24 pigs each, which were infected with either 100, 500 or 2 000 cercariae per pig. The 3 group s were further divided into 4 subgroups of 6 pigs each which were perf used with our selective technique at 4, 11, 17 or 24 weeks post infect ion, respectively. All of the pigs received an oral praziquantel treat ment prior to perfusion. The results indicated that increasing intensi ties and/or duration of infection resulted in trapping of schistosomes in intravascular inflammatory reactions which made it more difficult to collect the adult schistosomes by perfusion.